Approximately 85 percent of the Great Lakes shipping trade includes iron ore, coal and limestone. Additional tonnage is salt, cement, grain and oil. “NBC Nightly News” reports evaporation on the Great Lakes is outpacing precipitation, compromising water levels. The Lake Carriers Association reports for the 14th straight year, low water levels are affecting the $34 billion shipping industry. Three lakes remain below historical averages and in January, Lake Michigan and Lake Huron hit record lows, followed by the largest freshwater lake in the world, Lake Superior. Barge captains report draft levels of 2.5 to 3 feet, sometimes as low as 9 inches. Hydrologists believe a lack of snow and rain over the lakes in winter drastically reduced levels in addition to evaporation fueled by warmer water temperatures. Fastcast: Drier.